This research proposal seeks to delineate the pathophysiologic mechanisms involved in several of the presently unexplained hypoglycemic states in infants and children. Children will be studied in order to obtain information concerning the normal and metabolic adaptation to fasting, with particular emphasis on capacity for gluconoegenesis (including the availability of substrates for gluconeogenesis), availability of alternate metabolic fuels, and hormonal milieu. These age-grouped normals will then be contrasted with patients currently grouped under the umbrella diagnosis of "idiopathic hypoglycemia of infancy", including the major subgroup of ketotic hypoglycemia. Patients with hypopituitarism and hypoglycemia will also be studied.